1. Field of the Invention
The present invention relates to a photosensitive colored resin composition, a transfer material, and an image forming method, and more specifically relates to a resin composition and a transfer material for forming a colored image such as a color filter to be used in a liquid crystal display device or the like or a photomask to be used in a photolithographic process, an image forming method suitable for forming a colored image by a lamination method, and a color filter and a photomask thus obtained.
2. Description of the Related Art
Photosensitive resin compositions have long been used in various image forming materials. In particular, photosensitive colored resin compositions including a coloring component such as a dye or a pigment in such photosensitive resin compositions are widely utilized in forming various colored images such as a paint, an ink or a printing proof material.
Also a method of coating and drying a photosensitive resin composition in advance on a film support to form as a filmed resist, and transferring the photosensitive resin layer from the support to a substrate is called a transfer method, which has advantages that a thin film with a high quality can be formed highly efficiently. Such method is described for example in the JP-A (Japanese Patent Application Laid-Open) Nos. 5-39450, 5-72724, 6-80503 and 9-197665, and there is disclosed an example of forming a colored image such as a color filter by such method.
Also in recent years, this transfer method is also used in the uses requiring various resistances such as image hardness, chemical resistance, light fastness, scratch resistance and the like in the obtained image, such as a color filter employed in a liquid crystal display device or a mask material. For example, the color filter is required to have a high heat resistance, a high hardness and a high solvent resistance because it is subjected, in a panel forming process after the preparation of the color filter, to application of a transparent orienting film thereon and to a step of adhesion to an opposing substrate and injection of liquid crystal.
A Cr mask having a metallic chromium layer and an Em mask (emulsion mask) having a layer of silver halide emulsion are also known as the photomask material employed in a photolithographic process in the fields of the flat panel display, the shadow mask for CRT, the printed circuit board and the semiconductors, as described in “Photofabrication” (Japan Photofabrication Association, edited by Kyoiku Bunka Kai, pp67–80, June 1992).
The metal Cr mask is prepared by formation of a chromium layer by sputtering it on a transparent substrate such as of quartz or glass, then formation of an etching resist thereon by coating and the like, exposure for example with a HeCd laser (442 nm), patterning of the etching resist by development with aqueous alkali solution, etching of chromium and peeling of the etching resist. Such Cr mask has the advantages of defect repairability, high resolution, high durability (scratch resistance) and excellent washability, but is very expensive because of the complex preparing process thereof, and requires chromium etching in the preparing process thereby not only leading to a cost increase because of the required waste treatment but also being undesirable environmentally.
On the other hand, the Em mask can be prepared by providing a silver halide emulsion on a transparent substrate such as of quartz or glass, then exposure with a YAG laser or the like, development and fixation. Such photomask material requires only a small exposure energy (about 0.1 mJ/cm2) because of the high optical sensitivity of the emulsion, is environmentally safe and inexpensive. However, it cannot provide a very high resolution because silver halide is used as the photosensitive material, and is insufficient in durability because the photosensitive layer is composed of a gelatin film. Also the repairing of a defect in the photomask is practically difficult.
In consideration of the foregoing, there is desired a photomask material which is safe and inexpensive and has excellent durability (scratch resistance), and enables easy defect repairing.
In order to realize such various resistances in the photosensitive resin composition, there is generally utilized a negative composition which can improve the film strength in the image forming process including for example an imagewise exposure and a development. It is also effective to carry out a process after the image formation (such as a post-heating or a post-exposure) thereby further advancing the crosslinking or hardening reaction in the resin layer.
The negative photosensitive resin composition is generally composed of a binder resin, a photopolymerizable polyfunctional monomer, a photopolymerization initiator and the like. The binder resin is usually alkali developable, and generally includes an acidic group such as carboxylic acid. Various investigations have been made in order to improve the resistances after hardening of such resin compositions.
For example there is known a method using a thermal crosslinking agent which reacts with a carboxylic acid and the like in combination with the aforementioned resin component. More specifically, JP-A No. 57-178237 discloses a photosensitive resin composition including a binder (containing a carboxyl group), a polyfuntional monomer, a photopolymerization initiator and a compount containing at least two epoxy groups in a molecule, and JP-A No. 2000-181058 discloses a photosensitive resin composition including a resin containing a carboxyl group and an ethylenic unsaturated group, an epoxy resin, a photopolymerization initiator and an inorganic filler.
There is also known a case including such thermally crosslinkable group in the binder. For example JP-A Nos. 2000-81701 and 10-316721 disclose photosensitive resin compositions including a copolymer obtained from a monomer having a carboxyl group, a monomer having an epoxy group and another monomer.
However, though such compositions improve the strength of the hardened film by the exposure and the heating thereafter, they are insufficient in the stability with time, and have a drawback that the composition becomes hardened even prior to use thereof by the proceeding of a thermal reaction in the course of a prolonged storage.
In order to resolve such drawbacks, there is known a case employing a block isocyanate compound which is a precursor of an isocyanate group, as a new hardener. For example JP-A Nos. 3-50549, 7-278254, 8-15861, 10-20505 and 10-148938 disclose a composition including a binder resin having a carboxyl group, a polyfunctional monomer, a photopolymerization initiator, and a block compound of polyfunctional isocyanate. Though such hardeners have a significantly improved stability with time, in comparison with the conventional epoxy hardeners, but they are in fact inferior in the hardening property and are unsatisfactory in the resistances such as chemical resistance and hardness.
On the other hand, there is also investigated a method of introducing a reactive group, particularly a photopolymerizable functional group into the binder resin. Such binder resin is already known, and for example JP-B (Japanese Patent Application Publication) Nos. 50-34444 and 51-39847 and JP-A Nos. 53-097416 and 2-230154 disclose photosensitive resin compositions including a resin in which a polymerizable group is introduced by adding a compound having an epoxy group and a polymerizable group to a polymer having a carboxyl group. However, these methods are defective in that a compound having an epoxy group and a polymerizable group which involve concern in safety is used and in that such compound remains in the system because the aforementioned addition reaction is a reaction of high-molecule and scarcely proceeds completely.
Also the resin having a polymerizable group is widely employed in the solder resist. Representative examples include compositions utilizing a resin obtained by modifying novolac type epoxy resin as disclosed in JP-B No. 1-54390 and the like, and those utilizing a resin obtained by modifying a resin having an anhydride with a polymerizable compound having a hydroxyl group as disclosed in JP-A No. 2-23351 and the like. However these compositions basically include an epoxy compound as the thermal hardening component and are therefore insufficient in stability with time.
Also JP-A Nos. 2000-105456, 2000-250217 and 2000-298339 disclose examples of a composition employing an addition product of a polymer having a carboxyl group and a compound having a (meth)acryloyl group and an isocyanate group, and examples of application thereof to the color filter. However, also in this case, there is required an epoxy group in the resin or an epoxy resin as an additive component in order to ensure the hardening property, so that the stability with time is insufficient.
On the other hand, there is also disclosed a case not employing the thermally hardening component.
At first, with respect to the kind of the polymerizable group, for example the Japanese Patent No. 3120476 discloses a colored paste for color filter, utilizing a resin having a carboxyl group and a (meth)acryloyl group and including styrene as the copolymerization component, and JP-A No. 9-80225 discloses a resin having a carboxyl group and a cinnamoyl group or the like. Also JP-A No. 2000-154207 discloses a photosensitive resin composition for color filter, utilizing a resin having an acryloyl group and a carboxyl group. Also the JP-A No. 60-112035 discloses a solder resist including a linear polymer having a double bond in a side chain, and describes that a (meth)acryloyl group is preferable also in this case.
In addition to the foregoing, JP-A No. 49-120703 and JP-B Nos. 63-41923 and 1-7649 disclose examples of the photosensitive resin composition utilizing a resin having a reactive group such as an azide group, a cinnamate ester, a chalcone, a stilbazolium or a styryl quinolium.
However, among these conventional technologies considered in terms of the polymerizable reactive group, the most representative (meth)acryloyl group has a drawback of easily reacting at the stage of synthesis because of its high polymerizability but having a still insufficient hardening ability when introduced into the resin. Also the cinnamate ester, chalcone, stilbazolium or styrylquinoline results in a low sensitivity because of insufficient reactivity and cannot provide sufficient hardness and chemical resistance even after hardening. Also the azide group has explosivity during preparation.
Also with respect to the synthesizing method, JP-A 1-19572 discloses a photosensitive resin composition utilizing a resin formed by an addition of a compound having an epoxy group and a polymerizable group to a copolymer of (meth)acrylic acid and a (meth)acrylate having a specific ring structure. Also JP-A Nos. 63-40141 and 4-194941 disclose a photosensitive recording element and a colored image forming material utilizing a reaction product of a copolymer of (meth)acrylic acid with glycidyl (meth)acrylate. Further, JP-A Nos. 59-220731, 62-285903, 2001-66412, 2001-66772 and the like disclose photosensitive resin compositions utilizing a resin formed by addition of a compound having a hydroxyl group and a polymerizable group to a resin having an anhydride ring. There is also described an example (resin having a carboxyl group and a polymerizable group) utilizing a resin formed by reacting a maleic acid copolymer with a compound having a hydroxyl group and a polymerizable group (allyl, cinnamyl or (meth)acrylate) or a compound having an epoxy group and a polymerizable group (allyl, cinnamyl or (meth)acrylate).
However, among these conventional technologies considered in terms of the synthesizing method, the addition of a compound having a hydroxyl group and a polymerizable group to an anhydride can be most easily and most commonly achieved by a method of adding a compound having a hydroxyl group and a (meth)acryloyl group, but such method results in an insufficient hardening property as explained in the foregoing. Also the reactivity is similarly insufficient in the case of utilizing a cinnamyl group. In the case of utilizing an allyl group, the most common raw material is allyl alcohol, but this material is toxic and difficult to use in the manufacture. Also in the case of adding a compound having an epoxy group and a polymerizable group to a resin having a carboxyl group, such compound has a concern in terms of the safety.
The present inventors have found that an allyl group, which cannot be generally considered a compound having a high polymerizing ability, has an excellent hardening property after introduction into a resin, particularly has an excellent hardening property by heating after pattern formation, despite that such allyl group is stable during the synthesis thereof. It is further featured by the use of a resin capable of introducing the allyl group at a high content without utilizing a compound involving a concern on safety such as allyl alcohol or allyl glycidyl ether, and capable of being synthesized in a step. The present inventors also have found that a composition also excellent in the pigment dispersibility can be obtained while retaining the aforementioned characteristics, by utilizing a copolymer having a specific structural unit in combination with the allyl group.
The possibility of using an allyl group as a reactive group is already described in the JP-B Nos. 50-34444 and 52-48521, JP-A Nos. 59-220731, 1-19572, 2-23351, 5-281734, 7-325400, 8-101505, 10-90510, 2000-292615, 2001-66412 and 2001-66772 mentioned in the foregoing, and there are also disclosed therein examples of application thereof to a color filter or those containing a light-shielding pigment or an inorganic pigment. However, none of these references clearly describes the features of the effect of the allyl group, and a (meth)acryloyl group is merely described as effective as the reactive group in consideration of the polymerizability. A sufficient hardening property cannot be obtained with the resins specifically described in these references.
There is also disclosed an example of the color filter, utilizing a resin having a reactive group, without limitation on the type of the reactive group, for example in JP-A Nos. 6-11831 and 9-269409. However these references indicate a (meth)acryloyl group or the like as specific examples but lack the description on the allyl group. A sufficient hardening property cannot be obtained with the resins specifically described in these references.
There are also known other examples using a resin having an allyl group. JP-B Nos. 3-65542 and 5-2140 disclose a composition including a resin having a carboxyl group and an allyl group, a polymerizable monomer and a diazo resin. However such example is different from the invention because it requires a diazo resin as an essential component and is applied to a printing plate. Also JP-A No. 8-101498 discloses a photosensitive composition in which a pigment is dispersed with a resin having a polymerizable group in the side chain, and describes that an allyl group is effective for improving the sensitivity. However, this example is also limited to an application to a planographic printing plate, and lacks a description that the allyl group is effective in improving the hardness at baking.
Also JP-B No. 62-48819 discloses a negative resist utilizing a resin having both an allyl group and a hydroxyl group in a side chain. It is also described that the etching resistance is improved by baking. However this reference describes that the etching resistance is insufficient with the allyl group alone and lacks the description on the hardness of the obtained image or on the relaxation of the baking conditions. It also lacks the description on the alkali development.
JP-B No. 3-71705 describes a photosensitive resin composition utilizing a resin including dimethylallyl methacrylate as a constituent unit. However this example intends to form a distribution pattern in the refractive index by extraction of specific low molecular weight components, and is therefore different from the invention. Also JP-A No. 5-84894 discloses a composition comprising a resin having an allyl group, and an aromatic aldehyde or an aromatic ketone. However this example intends to form a pattern involving a difference in the refractive index and a relief by eliminating the aromatic aldehyde or aromatic ketone by a reduced pressure process or the like, and is therefore different from the invention.
As described in the foregoing, there has not been known a composition or a transfer material, that can simultaneously satisfy the requirements, such as satisfactory image forming properties including sufficient exposure sensitivity, alkali developability and resolution advantageously applicable to a color filter or a mask material, also that is excellent in the stability with time, hardening property, various resistances after hardening, and pigment dispersibility, and that requires only mild heating conditions for providing such resistances.